Valve devices of the above type can be used, for example, as exhaust gas return flaps or exhaust gas flaps. Such flaps can also be used as throttle flaps in air-conducting conduits. When using such valve devices as an exhaust gas return flap, the tightest possible closure of the channel in the closed state of the flap is required on the one hand, and, on the other hand, a good controllability of the volume flow is needed. Care must further be taken to obtain a sufficient thermal endurance in the hot exhaust gas tract.
There are various designs of such multi-part flaps which are intended to improve the sealing tightness in the closed state.
EP 1 455 124 A1, for example, describes a flap valve for a gas- or liquid-conducting conduit which is eccentrically supported and consists of a flexurally rigid element arranged on the outflow side and an elastic spring sheet arranged on the inflow side. In the housing, an abutment edge is formed which is abutted by the spring sheet in the closed state. In this arrangement, one half of the spring sheet has the same size as the flexurally rigid element, wherein this half is biased in a direction leading away from the flexurally rigid element so that the spring sheet, when laid onto the abutment edge, is pressed with tension against the abutment portion. The other half of the spring sheet is larger than the flexurally rigid element so that this side can also abut on the abutment portion formed in the opposite direction within the channel. A possible distortion of the spring sheet is restricted by the abutment of the flexurally rigid element.
EP 1 489 285 A2 describes a flap valve which can be used as a throttle flap and is made of two support plates and an elastomeric plate arranged between the support plates, the elastomeric plate extending on all sides beyond the periphery of the support plates and, in the closed state of the flap, abutting by its outer periphery on the inner wall of the channel. This flap, however, is not suited for use in the exhaust gas area because the elastomer does not have the required thermal endurance.
The disadvantages of the previous designs are that relatively high actuating forces are necessitated to safeguard a sufficient sealing tightness of the valve device in the closed state.